Method for the preparation of groups iii{14 v single crystal semiconductors

ABSTRACT

Method of making an intermetallic compound semiconductor composed of two elements, one of which is a group III metal which has a relatively low vapor pressure at the melting point of the desired intermetallic compound, and the other is a Group V element which has a relatively high vapor pressure at the same temperature which involves establishing a temperature differential along a confined fused mass of the first element and exposing the higher temperature surface of the mass to vapors of the high vapor pressure element, thereby simultaneously forming and growing at least a single crystal of the intermetallic compound at a lower temperature portion of the confined zone.

United States Patent Inventors Kunio Kaneko;

Naozo Watanabe, both of Tokyo, Japan Appl. No. 805,626 Filed Mar. 10, 1969 Patented Oct. 26, I971 Assignee Sony Corporation Tokyo, Japan Priority Mar. 8, 1968 Japan 43/15 1 16 METHOD FOR THE PREPARATION OF GROUPS III-V SINGLE CRYSTAL SEMICONDUCTORS 5 Claims, 1 Drawing Fig.

US. Cl 23/204, 148/ l .6 Int. Cl C0lb 27/00, B0 l j 17/00 Field of Search 23/204 R; 148/ 1.6, 175

I I I I I I I I I I I I I I I I I [56] References Cited UNITED STATES PATENTS 3,366,454 l/l968 Folberth et al. 23/204 FOREIGN PATENTS l ,063,084 3/l967 Great Britain 23/204 Primary Examiner0scar R. Vertiz Assistant Examinerl'loke S. Miller Attorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT: Method of making an intermetallic compound semiconductor composed of two elements, one of which is a group III metal which has a relatively low vapor pressure at the melting point of the desired intermetallic compound, and the other is a Group V element which has a relatively high vapor pressure at the same temperature which involves establishing a temperature differential along a confined fused mass of the first element and exposing the higher temperature surface of the mass to vapors of the high vapor pressure element, thereby simultaneously forming and growing at least a single crystal of the intermetallic compound at a lower temperature portion of the confined zone.

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IampemIr/ve (P0 I I I I I I I I I I I I I I I I METHOD FOR THE PREPARATION OF GROUPS III-V SINGLE CRYSTAL SEMICONDUCTORS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is in the field of making intermetallic semiconductor elements of the type represented, for example, by the combination of a metal from Group III of the Periodic System and a metalloid of Group V. The invention is con cemed with the simultaneous formation and growth of a single crystal intermetallic compound by means of vapor diffusion of the metalloid into a fused mass of the metal under controlled conditions.

2. Description of the Prior Art There have been many attempts made to produce a single crystal semiconductor of the intermetallic compound type to be used as a substrate for luminescent diodes, transistors, diodes and the like. These intennetallic compounds are formed by the combination of a metal of Group III of the Periodic Table and a metalloid of Group V. Since these elements have a vastly different vapor pressure at a given temperature, there is a great deal of difficulty encountered in the formation of a single crystal of the intermetallic compound, particularly one large enough to be used as a substrate for semiconductor devices. Furthermore, the reproducibility of prior art processes is rather poor.

The melting point of a typical intermetallic compound semiconductor, gallium phosphide is approximately 1,450 C. and its decomposition pressure is measured in ls of atmospheres. It has been proposed to achieve single crystal growth of this intermetallic compound by means of high temperatures, but this method is defective because impurities are likely to contaminate the compound.

Although it is possible to grow a single crystal from a gallium phosphide melt at relatively low temperatures, below about l,200 C., this procedure requires about times an amount of gallium as theoretically required for the formation of the compound, and the reproducibility of the process is low.

SUMMARY OF THE INVENTION The present invention provides a method for the manufacture of a single crystal intermetallic compound semiconductor wherein the constituent having the relatively low vapor pressure is fused in a confined zone, after which a temperature differential is applied along the fused mass such that one portion of the fused mass is at a significantly higher temperature than another portion of the same fused mass. While these conditions of temperature are maintained in the fused mass, the more volatile, higher vapor pressure element is vaporized and the higher temperature portion of the fused mass is exposed to the vapors of this element. This results in a reaction between the two to form the intermetallic compound which then grows as a single crystal from the lower temperature portion of the confined zone.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing shows somewhat schematically a furnace assembly which can be used for the purpose of the present invention, alongside of which there is a graphical representation of the temperatures existing at various portions of the furnace.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description will be made in conjunction with the manufacture of gallium phosphide but it should be understood that similar techniques can be used in the manufac ture of other intermetallic type semiconductors such as gallium arsenide, indium phosphide, indium arsenide and the like.

In the drawing, reference numeral 1 indicates a vacuum container composed, for example, of quartz. A crucible 2 tion thereof. The particular crucible shown in the drawing is generally conical in shape and has a pointed lower end 2a as shown in the drawing. The relatively low vapor pressure material, gallium in the example given, is fused in the crucible 2 to provide a melt 3. A supply of red phosphorous 6 is placed at the bottom of the vacuum container 1. Heating of the gallium and of the phosphorous may be conducted independently by providing separate electric furnaces 4a and 4b, respectively for each of the two materials. The temperature of the upper surface 3a of the molten gallium is held, for example, at about 1,200 C. which is below the melting point of the desired intermetallic compound, gallium phosphide. The temperature at the lower-end 2a of the crucible 2 is held at a temperature which is lower than that of the upper end by 20 to 300 C. Eypically, the temperature at the lower end 2a is about i, 1 50 The temperature of the phosphorous 6 is such that it has a vapor pressure which exceeds the decomposition pressure of the gallium phosphide to be produced. As shown in the graph which forms part of the figure, the temperature of the phosphorous may be about 450 C., while the temperature of the molten gallium may range from l,l50 C. near the bottom of the crucible to l,200 C. at the top of the crucible.

Since phosphorous boils at about 280 C., there will be a very substantial vapor pressure of phosphorous existing in the enclosure, and the phosphorous vapors will diffuse into the molten gallium through the exposed upper surface 311 to form the compound gallium phosphide. The resulting intermetallic compound diffuses into the fused gallium toward the lower temperature portion, that is, the lower end 20 of the crucible 2 where gallium phosphide is reduced in the form of a single crystal 7. Continued application of heat causes further diffusion and growth of the single crystal so that formation of the crystal and growth occur in the same operation.

The following specific examples illustrate a variety of conditions under which the intermetallic compound semiconductors can be produced.

EXAMPLE 1 With the type of assembly illustrated in the drawing, red phosphorous was heated up to 1,450 C. to provide a vapor pressure of phosphorous in the container 1 of 1,400 mm. of mercury. The temperature on the surface 34 of the gallium 3 was l,l00 C., and at the lower end 2a of the crucible, the temperature was 1,060 C. The distance between the lower end 2a of the crucible 2 and the surface 30 of the gallium 3 was about 10 mm. After 5 days of reaction, a single crystal of gallium phosphide having a diameter of 12 mm. and a height of 12 mm. was obtained.

EXAMPLE 2 In this example, the distance between the surface 30 of the gallium and the lower end 2a of the crucible was about 14 mm. The temperature on the surface 3a was 1,1 15 C. and that at the lower end 2a of the crucible was 1,060 C. After 5 days reaction time, a single crystal having a diameter of 15 mm. and a height of 10 mm. was produced.

EXAMPLE 3 The temperature of the phosphorous was 430 C., and its vapor pressure was 700 mm. of mercury. The temperature on the surface 3a of the gallium was 1,170 C., and the temperature at the lower end 2a of the crucible 2 was l,l 15 C. The distance between the surface 3a of the gallium 3 and the lower end 2a of the crucible 2 was 12 mm. After 5 days, a polycrystal having a diameter of 12 mm. and a height of 13 mm. was obtained.

EXAMPLE 4 In this example, the temperature on the surface 3a of the fused gallium 3 was l,l70 C., and the temperature at the lower end 2a of the crucible was l,l30 C. The distance between the surface 3a and the lower end 20 of the crucible 2 was l2 mm. Otherwise, the conditions were those specified in example 3. In this case also, a polycrystal was produced.

The temperature on the surface 3a of the gallium should be high enough to provide for efficient reaction speed, but not so high as to exceed the melting temperature of the gallium phosphide. Furthermore, if the temperature is too high the vapor pressure in the container is so high as to necessitate the use of an expensive high pressure container. For example, at l,450 C., the container 1 is required to withstand a vapor pressure of about 30 atmospheres. Consequently, it is desirable that the temperature on the surface 3a of the fused gallium be no higher than about l,300 C. n the other hand, too low a temperature requires an excessively long reaction time and therefore the temperature should be at least l,l00 C.

The diffusion velocity of the product increases with an increase in the temperature differential between the upper and lower portions of the crucible 2 and as a result increases the reaction speed. However, since the reaction speed is related to the vapor pressure of the phosphorous, too great a temperature differential is not desirable, and the temperature differential should not normally exceed 300 C. On the other hand, with too low a temperature differential, the reaction speed is substantially decreased. Accordingly, it is desirable that there be a temperature differential at least 20 C. to provide practical reaction speeds.

It should also be borne in mind that at lower temperatures, single crystal growth is rendered difficult. Accordingly, in the case of gallium phosphide, temperatures below 800 C. are not desirable at the lower end of the crucible, as illustrated by examples Ill and IV.

As far as vapor pressure of the phosphorous is concerned, the use of an excessively high vapor pressure provides a problem of container design, as mentioned previously, while too low a vapor pressure reduces the reaction velocity. It is accordingly preferred to use a vapor pressure in the enclosure of from l/lO to 30 atmospheres. The pressure should, however, be greater than the decomposition pressure of the gallium phosphide on the surface 3a of the gallium.

in these examples, the heating of the crucible took place by means of an electric resistance furnace. It can also be accomplish'ed in the following manner. A carbon crucible can be [Oil used instead of the quartz crucible 2, or a carbon susceptor is disposed outside of the crucible 2 and a coil is placed around the container 1. The carbon is then heated by high frequency heating currents to heat the crucible.- The crucible may also be made of boron nitride to eliminate the possibility that oxygen or silicon from the quartz could enter the resulting crystal. In order to diffuse suitable impurities into the crystal such as zinc, oxygen, cadmium, tellurium or the like, these elements may be added to the fused gallium 3. In order to maintain a temperature distribution in the crucible at desired values, the crucible or the electric furnaces may be axially shifted.

in the preferred embodiment of the invention, a vaporous atmosphere of phosphorous is produced in the sealed container but it is also possible that the crucible can be placed in a nonsealed tube and phosphorous containing gases such as phosphine, phosphorous chloride and the like passed over the surface of the fused gallium using hydrogen as a carrier gas.

It should be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

We claim as our invention:

1. The method of making an interrnetallic compound semiconductor composed of a first element from Group III having a relatively low vapor pressure at the melting point of said compound and a second element from Group V having a relatively high vapor pressure at said melting point which comprises fusing said first element in a confined zone, applying a temperature differential along the fused mass of between 20 and 300 C. while maintaining the fused element at a temperature below themeltin point of the desired intermetallic compound, vaporizing sai second element, and exposing the higher temperature portion of said fused mass to the vapors of said second element to thereby form a single crystal of said intermetallic compound at a lower temperature portion of said zone.

2. The method of claim 1 in which said first element is galli- 3. The method of claim 1 in which said second element is phosphorous.

4. The method of claim 1 in which said first element is gallium and said second element is phosphorous.

5. The method of claim 4 in which said higher temperature portion is at a temperature from l,l00 to l,300 C. 

2. The method of claim 1 in which said first element is gallium.
 3. The method of claim 1 in which said second element is phosphorous.
 4. The method of claim 1 in which said first element is gallium and said second element is phosphorous.
 5. The method of claim 4 in which said higher temperature portion is at a temperature from 1,100* to 1,300* C. 